This invention relates generally to multi-wavelength optical monitors and more particularly to optical signal monitors in dense wavelength division applications.
The rapid adoption of the Internet has created a need for high-speed optical networks. The deployment of these networks has been hindered by a lack of optical components. These components tend to be difficult to build mainly due to the precise tolerances needed to achieve good optical coupling.
An area that has shown promise in alleviating the manufacturing bottleneck is integrated waveguide technology. Waveguides can be formed using similar processes to those used for manufacturing integrated circuits. This allows for mass production of precise components. Unfortunately, two main problems result. First, the waveguide devices are often temperature sensitive requiring special packaging considerations and, second, it is difficult to couple light into and out of the waveguide device absent substantial losses.
An optical monitor is a critical component in optical networks. Typically optical monitors accompany multi-wavelength fibre optic amplifiers, such as erbium doped fibre amplifiers; the optical monitors are used for providing feedback to the amplifiers or to a controller. They are also useful in ensuring maintained coupling efficiencies and in test equipment for optical communication equipment.
Conventional optical monitors for multi-wavelength fibre optic communication needs come in a variety of different configurations. In U.S. Pat. No. 6,078,709 an optical monitor is demonstrated. The monitor has a grating in a fibre for deflecting a portion of light propagating within the fibre out of the fibre. This deflected portion is then detected with a detector. The grating achieves multi-wavelength behaviour through application of heat in order to vary its frequency response. As the grating expands, the wavelength of light that it deflects changes. By controlling the temperature precisely a known wavelength is monitored precisely. This design has the benefit of being able to monitor any wavelength within a given range, however it is only capable of supporting monitoring of one wavelength channel at a time. Further, a precise heating element is required to provide adequate performance.
Another common method for performing multi-wavelength monitoring is to tap off some of a light signal and to use a wavelength dispersing element in order to separate the light such that light within each channel is incident upon a different detector from a plurality of optical detectors. This device has the advantage that all of the wavelengths are monitored at once. Unfortunately, such a device is often produced in bulk optics and is hampered by the above-mentioned manufacturing bottlenecks. When manufactured with integrated optical technology, the resulting demultiplexer has many output ports for coupling to fibres and, as such, is extremely difficult to manufacture.
The prior art is limited in that the optical connections between the various components must be very accurate to ensure that the optical signals are not overly attenuated before reaching the monitor. Of course, if all errors were identical, the monitor error would be less significant but, since each alignment error is somewhat unknown, the resulting errors compound to render such a monitoring device unreliable on the one hand and overly costly to produce on the other.
Additionally, errors in coupling contribute to other known issues such as polarisation-dependent loss (PDL), which becomes a factor in the monitor efficiency and accuracy.
Since prior-art multi-wavelength monitors rely on a wavelength division demultiplexingxe2x80x94either using a single filter to drop one wavelength or a dispersive element to demultiplex the channelsxe2x80x94to produce specific wavelength output signals they are subject to wavelength drift in the demultiplexer due to temperature changes. Currently, this is compensated for by mechanically moving the input fibre as the temperature varies. Alternatively, the demultiplexer is heated to a constant temperature. Either solution is effective but increases the cost and complexity of the monitor.
Another disadvantage of the prior art is that it results in a monitor having fixed characteristics. For example, a 32-channel monitor is limited to that exact function. Even when 32 channels monitors are obsolete or when different channel allocation is used, the monitor, because its characteristics are formed in the physical component, is limited to the original 32 channel applications.
In order to overcome these and other shortcomings of the prior art it is an object of the invention to provide an optical wavelength monitor absent a need for extremely precise alignment needed in conventional optical components.
This invention relates generally to optical monitors and more particularly to the optical-alignment and the production of optical signal monitors for dense wavelength division applications.
In accordance with the invention there is provided a method of fabricating an optical component comprising the steps of:
providing a detector array having more detectors than a number of known channels;
providing an input port and a dispersive element within a waveguide structure, the dispersive element disposed for receiving light provided at the input port and for dispersing the light onto the detector array, the light dispersed other than as channelised data within the known channels; and,
determining a mathematical model for transforming light detected by the detector array into values indicative of intensity of light within each of the predetermined wavelength ranges corresponding to the known channels.
In accordance with another embodiment of the invention, there is provided a method of fabricating an optical component having an input endface comprising the steps of:
providing a dispersive element within a waveguide structure, the dispersive element disposed for receiving light provided at a input endface of the waveguide structure and for dispersing the light onto an output endface of the waveguide structure, the light dispersed other than as channelised data within known channels;
affixing a detector array having more detectors than a number of the known channels to the output endface of the waveguide;
electrically coupling the detector array for providing detected data to a processor for processing thereof, and,
determining a mathematical model for transforming light detected by the detector array into values indicative of intensity of light within each of the predetermined wavelength ranges corresponding to the known channels, the transfer function accommodating imprecise placement of the detector array and variations in a location on the input endface where light is received.
In accordance with another aspect of the invention, there is provided an optical component comprising:
an input port;
a detector array having more detectors than a number of known channels; a waveguide structure including a dispersive element within the waveguide structure, the dispersive element disposed for receiving light provided at the input port and for dispersing the light onto the detector array, the light dispersed other than as channelised data within the known channels; and
a processor for transforming light detected by the detector array into values indicative of intensity of light within each of the predetermined wavelength ranges corresponding to the known channels, using a mathematical model of that relationship, the model accommodating imprecise placement of the detector array.
In accordance with the further aspect of the invention, there is provided an optical component comprising:
a waveguide structure including: an input endface, an output endface; and a dispersive element, the dispersive element disposed for receiving light provided near a predetermined location on the input endface of the waveguide structure and for dispersing the light about a location on the output endface near a predetermined location, the light dispersed other than as channelised data within known channels;
a detector array having more detectors than a number of the known channels disposed adjacent the output endface about the predetermined location for providing signals based on detected light; and,
a processor for transforming data into values indicative of intensity of light within each of the predetermined wavelength ranges corresponding to the known channels, using a mathematical model of that relationship, the model making possible numerical compensation for at least one of imprecise placement of the detector array and variations in a location on the input endface where light is received.
The ability to use substantially coarse alignment without affecting the quality of monitoring the device is capable of performing is extremely advantageous. Further advantageously, thermal compensation can be performed by processing of the detected optical signals.